A winding method of a typical stator coil in the related art of a rotating-field electrical rotating machine adopts a configuration such that lessens a voltage phase difference between winding circuits by placing one winding circuit as close as possible to the other winding circuit in parallel circuits of a same phase. However, even when the winding circuits are placed in close proximity to each other, displacement at least as wide as one stator slot is generated, and a non-negligible voltage phase difference occurs between the winding circuits. A circulation current flows between the winding circuits due to the voltage phase difference. Hence, there is a problem that the occurrence of a circulation current loss gives rise to a temperature rise of the stator coil and deterioration in efficiency of the electrical rotating machine.
An example of a method of eliminating such imbalance in voltage phase and magnitude between the winding circuits forming the parallel circuits is described in PTL 1 as an armature winding pattern for a multi-phase power generator, and this method aims for a winding pattern of a two-layer lap winding. According to this method, in a lap winding for a multi-phase electrical machine with two or more circuits per pole per phase, a circuit order of coil sides in a top layer of a given phase band and a circuit order of coil sides in a bottom layer of the same phase band are changed by varying pitches of respective other coils within one circuit. According to this winding pattern, the circuit order of all the coil sides in a given layer (top layer or bottom layer) of a given phase band is exchanged with the circuit order in the other layer (bottom layer or top layer) of this phase band. Consequently, imbalance in phase and magnitude of composite voltages generated in the respective parallel circuits of the each phase winding is substantially eliminated.
There is also a method for an armature described in PTL 2. A 72-slot armature core and a three-phase, two-pole, four-parallel-circuit armature winding stored in the slots are connected in the following manner. That is, let relative positions of a upper coil piece and a lower coil piece in one of phase bands be indicated by positions counted in a direction away from a pole center, then the upper coil pieces and the lower piece coils in first and third parallel circuits are at first, fourth, sixth, seventh, tenth, and twelfth positions from the pole center, and the upper coil pieces and the lower coil pieces in second and fourth parallel circuits are at second, third, fifth, eighth, ninth, and eleventh positions. Owing to the connection as above, insulation properties and fixing strength can be more readily secured by making a work with a jumper wire connection portion easier when the armature winding is formed while reducing a circulation current loss between the parallel circuits by lessening imbalance in voltage among the respective parallel circuits.
Further, there is a method for an armature winding of an electrical rotating machine described in PTL 3. This armature winding is a two-layer, four-parallel-circuit armature winding with 14 coils per pole per phase applied to a three-phase, two-pole, 84-slot electrical rotating machine. Each phase band of the winding has two parallel circuits and stored in a slot 13 provided to a laminated core. Each parallel circuit has series coils and each series coil has two coil pieces; an upper coil piece 15 and a lower coil piece 16 connected to each other at a coil end 19a on a connection side and a coil end 19b on an opposite side to the connection side. Let relative positions of the upper and lower coil pieces in one phase band be indicated by positions counted from the pole center, then halves of the respective parallel circuits are connected so that the upper and lower coil pieces are positioned at first, fourth, sixth, seventh, ninth, twelfth, and fourteenth positions from the pole center, and the remaining halves of the respective parallel circuits are connected so that the upper and lower coil pieces are positioned at second, third, fifth, eighth, tenth, eleventh, and thirteenth positions from the pole center. Owing to the connection as above, a circulation current loss between the parallel circuits is reduced by lessening imbalance in voltage among the respective parallel circuits.